1. Field of the Invention
The invention relates to a magnetooptic recording medium for recording and/or reproducing information by a laser beam or the like by utilizing a magneto-optical effect and, more particularly, to a magnetooptic recording medium of an artificial lattice film system having a good vertical magnetic anisotropy and a high coercive force.
2. Related Background Art
In recent years, as a rewritable high density recording method, a magnetooptic recording medium for performing recording and reproduction by a semiconductor laser beam or the like has been highlighted.
Hitherto, as a magnetic material which is used in the magnetooptic recording medium, there has been used an amorphous alloy comprising a combination of a rare earth element such as Gd, Tb, Dy, or the like and a transition metal element such as Fe, Co, or the like. However, there is a drawback in that the rare earth elements and Fe which construct the amorphous alloy are easily oxidized and corrosion easily occurs under a hot and humid environment.
On the other hand, a recording material of the Co-Pt system or Co-Pd system using a platinum group metal such as Pt, Pd, or the like in place of the rare earth element has excellent corrosion resistance. Techniques for raising the coercive force by using those systems as artificial lattice films are disclosed in JP-A-1-98144, JP-A-1-162257, and the like. According to those techniques, in a range of an extremely thin film thickness of about 200 .ANG., a coercive force of about 100 to 200 Oe is obtained in case of the artificial lattice film of the Co-Pt system and a coercive force of about 500 to 2000 Oe is obtained in case of the artificial lattice film of the Co-Pd system, so that vertical magnetic films are realized. The artificial lattice film is what is called a super lattice film or modulation structural film, and is a film in which a plurality of layers which are made of different components and have a thickness of several tens of atomic layers or less are regularly repetitively laminated so as to each have a predetermined thickness.
The conventional magnetooptic recording medium using the foregoing artificial lattice film as a recording layer has a problem in that the magnitude of the coercive force of the recording layer and the magnitude of the vertical magnetic anisotropy are still insufficient to stably execute a magnetooptic recording.